The invention relates to a honing or grinding tool, comprising a cutting element, a cutting element support for the cutting element, and a measuring device for measuring wear of such tools.
Such tools are known. They are tools for machining by chip removal wherein a cutting layer (cutting element) is disposed on a steel base (cutting element support) by means of an adhesive layer.
In connection with the installation of fully automatic machining operations, primarily with multi-spindle machines, monitoring for wear is of great importance for operational safety and manufacturing quality. Wear of a honing bar is to the greatest extend dependent on the number of pieces machined (tool life quantity). Other effects are, for example, feed, material hardness or non-homogeneity of the tool. Tool replacement at the right time is very important for efficient manufacturing. It should not be performed too early, i.e. when the volume of the cutting means (volume of the cutting element or cutting layer) has not yet been fully used up; nor should it be performed too late, because this would mean a run with tools no longer of qualitatively high value, i.e. rejects.
Up to now it was possible to monitor the wear of the cutting element of a honing bar or a grinding wheel, for example approximately, in that in the simplest case the shortest tool life (time for machining one work piece) or tool life quantity (number of the work pieces machined) was determined and this value was made the standard for checking of the machine tool by the operators at corresponding intervals. Checking itself was performed by visual inspection of the tool.
Another possibility, in case of electronic-mechanical or electronic-hydraulic feed of the tools, lies in monitoring the feed travel. However, this means only indirect checking of wear of the cutting layer of a honing bar. If feeding is performed in steps by means of a defined number of pulses, it is possible, corresponding to the assumed wear, to also provide after a predetermined number of work cycles fixed predetermined number of additional feed pulses. Such a device also does not constitute actual wear monitoring, but merely compensation for wear. Only the sum of the additional pulses required for compensation and the comparison with an empirically set useable thickness of the cutting layer of a honing bar, however, will result in information as to whether replacement of a honing bar is needed, which can be processed by an automatic control.
In modern automatic controls the usable thickness of the cutting layer, the number of steps per compensating operation and the approach angle of a honing tool are input in the control. The machine is stopped when it reaches the wear limit, based on the addition of the compensation distance. The wear condition of the honing bars is displayed on a monitor by means of bar graphs. When reaching a programmable warning limit the automatic control alerts the operator in good time to replace the tool. However, this tool wear monitoring can only be employed in case of feeding by means of a step motor. This indirect wear monitoring cannot be used with hydraulic feeding. Furthermore, this indirect monitoring has the disadvantage of having to take into account manufacturing tolerances in regard to height. But such a height may under certain circumstances correspond to a tool life quantity of up to several thousand work pieces. Thus indirect wear monitoring does not guarantee the best possible efficient use of the cutting layer.
No honing bars are known in which the wear condition can be directly determined. Tools for machining of workpieces by chip removal are known from related fields, where wear monitoring is performed. However, the technologies used there cannot be directly used for the manufacture of a honing bar in connection with which direct wear monitoring can be performed.
For example, in EP-A-0 225 300 a throw-away carbide indexable insert is described, where a layer impervious to radiation is disposed on a substrate emitting radiation. With increased wear the substrate emitting radiation is increasingly exposed in the area of the flank. The radiation emitted by the substrate is determined as a measurement of wear. It is furthermore known from this reference to detect wear over small areas of the crater-wear type on the cutting edge itself. The direct wear monitoring by way of flank wear is impossible to apply in connection with honing bars, because they are in contact with the workpiece over large areas and have no flanks on which wear could be detected in this manner.
The same is true for DD-A-222 414. A method for detecting wear of a lathe chisel is described, in which a dot-shaped radioactive marker is applied to the flank and/or cutting edge of the tool. The radioactive marker wears off along with general wear. The change in radiation caused by this is used to measure wear. Aside from the not inconsiderable radiation exposure of the work place, such wear measuring is not usable with honing bars, because two-dimensional monitoring of the cutting element is not possible.
It is known from the German Journal "Fertigungstechnik und Betrieb" [Manufacturing Techniques and Operation] (1985) 9, pp. 523-526, in particular page 524, to coat the flank of a throw-way carbide indexable insert with a radioactive marking. Again, Wear detection takes place by measuring the flank wear. This method, too, besides the radiation exposure, is not usable for honing bars because these have no flanks. The same holds true for the measuring principle, alternatively cited in this publication, for the application of guideway structures at the flanks, which give off a signal when bonding because wear occurs. Honing and grinding tools are both tools with undeterminate cutting geometry in which flanks generally do not exit, contrary to throw-away carbide indexable inserts, drill or lathe chisels.
A drill is known from U.S. Pat. No. 4,420,253, into the shaft of which a glass fiber has been inserted. One end of the glass fiber is illuminated by a light source. The other end extends into the shaft and terminates at a set distance from the cutting edge. After the material located between the fiber end and the cutting edge has worn off, the light is registered in a detector located underneath the drill. Wear monitoring of a homing bar is not possible with such a method, because the entire area of the cutting element could only be monitored at excessive cost.
From German Published, Non-examined Patent Application DE-OS 34 04 257 a measuring device is known for measuring the wear on a knife for cutting semiconductor plates. In this publication the light beam, originating in an emitting device and reflected by the knife, is registered in a detector. Wear of the knife element results in a change of the reflective behavior of the knife. For this reason the intensity of the reflected light beam also changes. This measuring device has the disadvantage of being very susceptible to scattered light of other radiation sources. As recited in this reference, the measuring device does not function if the knife is wetted by a rinsing and/or cooling media. Furthermore, the measuring device only supplies a signal, because of the rotation of the knife, corresponding to a mean wear detected over a partial area of the knife.
Even if the mentioned disadvantages were accepted, such a method would in principle not be usable for honing and grinding tools, because wear of these tools cannot be definitely assigned to the reflective behavior of the cutting element at the time, otherwise determinable with relative accuracy, when they need to be replaced.
In U.S. Pat. No. 4,031,368 a measuring device on a machine tool is described wherein a laser beam is guided across the tool. The reflection of the laser beam is registered in a receiver arrangement and passed on to an evaluation device. This evaluation device computers wear from optical measurement data, combined with other parameters (for example, size of the workpiece, vibrations, roughness of the surface, and the like). This measuring device requires expensive and maintenance-intensive devices, such as a laser resonator. For the reasons already mentioned above, it is not useful for detecting wear on honing bars.